Conventionally, a fuel supply system which supplies fuel to an engine is equipped with a high-pressure pump which pressurizes the fuel suctioned from a fuel tank. The pressurized fuel discharged from the high-pressure pump is accumulated in a delivery pipe and is injected into a cylinder through an injector. Generally, a high-pressure pump is installed on an engine head. The high-pressure pump is comprised of a plunger and a cylinder. The plunger reciprocates in the cylinder to pressurize the fuel in a pressurization chamber.
Such a high-pressure pump receives heat from the engine, which may cause a deformation of the cylinder. The deformation of the cylinder gradually increases frictional heat between the cylinder and the plunger. It is likely that seizure may occur between the cylinder and the plunger. If the seizure occurs, a fuel pressure in a delivery pipe may be decreased and no fuel may be injected through a fuel injector. Finally, the engine may be stopped.
Patent Document 1 (JP-2008-2361A) shows that a high-pressure pump has a cylindrical bush made of heat-resistant material. This cylindrical bush is provided to a pump body through a cylinder holder and functions as cylinder, whereby a deformation of the cylinder is restricted.
Patent Document 2 (JP-2003-35239A) describes that a cylinder holder is made of material whose thermal conductivity is small and a thread portion of the cylinder holder is coated with resin, whereby heat transfer from a pump body to a cylinder is restricted.
Patent Document 3 (JP-2008-525713A) and Patent Document 4 (DE-10322599A) show that a cylinder is made of material which has high heat-resisting property, whereby it is restricted that the cylinder is deformed.
Patent Document 5 (JP-2010-106741A) shows a high-pressure pump which has a variable volume chamber on an opposite side of a pressurization chamber. A cylinder has a plurality of grooves on its outer surface. The fuel flows in and flows out from the variable volume chamber through these grooves, so that the cylinder is cooled by the fuel.
Patent Document 6 (US-77079966B2) shows a high-pressure pump which has a cylindrical clearance gap around a cylinder. This cylindrical clearance gap communicates with a pressurization chamber and a low-pressure fuel passage.
In the high-pressure pump shown in Patent Documents 1-4, a cylinder, a cylinder holder and a pump body are formed from separate pieces, which increases a number of parts. Further, the cylinder holder is made of low-heat-conductivity material and the thread portion of the cylinder holder is coated with resin material, which make the structure complicated and increases manufacturing steps.
Also, since the cylinder, the cylinder holder and the pump body are in contact with each other on their outer surfaces, it is likely that engine radiant heat may be transferred from the pump body to the cylinder.
In the high-pressure pump shown in Patent Document 5, since the grooves are formed around only one end portion of the cylinder, the entire cylinder is not always cooled.
The high-pressure pump shown in Patent Document 6 has no variable volume chamber. The cylindrical clearance gap communicates with only the low-pressure fuel passage. Thus, it is less likely that the fuel circulates to cool the cylinder.